Transport refrigeration units or systems condition the air of cargo spaces associated with straight trucks, tractor-trailer combinations, refrigerated containers or "reefers", and the like. The usually high value of the cargo in the conditioned load space of the associated vehicle makes it important that transport refrigeration systems be highly reliable. However, even the most reliable transport refrigeration system is subject to occasional malfunction, and thus it is also important that monitoring methods and apparatus be employed that will provide a very early indication of a malfunction, and the nature of the malfunction. It is also important that such indication of a malfunction, and its nature, be communicated to the proper personnel, so that steps may be taken to correct the problem before damage to the conditioned load occurs. At the very least, a malfunction alarm should be communicated to a person directly in charge of the transport refrigeration system, such as to the driver of a truck or tractor-trailer. Since remote monitoring of transport refrigeration units via radio and satellites is now utilized by some trucking companies, it is further important that the format of any alarm communication system be compatible with, and suitable for, use with such remote monitoring systems.
Thus, it would be desirable, and it is an object of the present invention, to provide new and improved monitoring methods and apparatus for transport refrigeration systems which provides a very early indication of a possible malfunction, along with an indication of the nature of the malfunction. It is also desirable, and is another object of the invention, to provide the status of the monitored unit in a format suitable for transmission to a display in the cab of an associated vehicle, and also suitable for radio communication to a site remote from the location of the transport refrigeration system being monitored.